The present invention relates to the medical diagnostic imaging and surgical arts. It finds particular application in conjunction with image guided surgery (IGS), and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other like applications.
Medical diagnostic imaging is a valuable tool for obtaining accurate visualization of a particular patient's internal anatomy and/or pathology in a minimally invasive manner. Prior to a medical procedure, three-dimensional (3D) diagnostic image data of the brain, spinal cord, and/or other anatomy of interest is often generated by computed tomography (CT) scanners, magnetic resonance imaging (MRI) scanners, gamma cameras, and other medical diagnostic imaging equipment. Typically, these imaging modalities provide structural detail with a resolution of a millimeter or better. Images, such as slices, 3D renderings, or projections, of the patient's anatomy are reconstructed and displayed on a video monitor and then used by medical personnel to aid in navigating through and/or around various anatomical structures. The displays are typically mounted displaced from the surgically sterile region surrounding the patient.
Various frameless stereotactic IGS procedures have been developed which take advantage of the 3D image data of the patient. These procedures include guided-needle biopsies, shunt placements, craniotomies for lesion or tumor resection, and the like. Another area of frameless stereotaxy procedure which requires extreme accuracy is spinal surgery, including screw fixation, fracture decompression, and spinal tumor removal.
In spinal screw fixation procedures, for example, surgeons or other medical personnel drill and tap a hole in spinal vertebra into which a screw is to be placed. The surgeon often relies heavily on his own skill in placing and orienting the bit of the surgical drill prior to forming the hole in the vertebra. Success depends largely upon the surgeon's estimation of anatomical location and orientation in the operative field. Unaided, this approach can lead to less than optimal placement of screws which in turn may injure nerves, blood vessels, or the spinal cord.
Nevertheless, use of a stereotactic IGS procedure presents certain problems and/or complications of its own. For example, one problem associated with common IGS systems is that the interventionalist is forced to continually switch his attention between a display showing the medical diagnostic image and the actual subject where he is working. Physically, over time, the continual switching of attention can lead to eye strain and/or fatigue. Moreover, mentally, it can be quite distracting and/or disruptive to the interventionalist's concentration.
Typical registration methods involve establishing a relationship between the patient space and image space. This is accomplished by the identification of three or more points in each space which define the transformation matrix between patient space and image space. Typically, the points used are anatomical markers, such as, for example, the nasium (bridge of the nose) and ear lobes. Alternatively, adhesive fiducial markers are affixed to the patient prior to imaging and identified by the operator in the diagnostic images. Consequently, the methods employed in the prior art are potentially error prone insomuch as they require the internal anatomy be in the same position relative to the external markers at the time of the diagnostic scan and throughout the registration process and interventional surgical procedure. Since this cannot be guaranteed except in those anatomical locations where the internal anatomy is closely held or fixed in position, such as, for example, in the brain and spinal vertebrae, the prior art has limited use for only a number of interventional procedures.
Moreover, while these markers assist in registering the patient to the electronic images, they do not directly mark anatomical features on the subject. Marking of these anatomical features on the patient is more difficult. This difficulty is compounded because the anatomy of interest is typically below the patient's surface and cannot be seen directly by the surgeon. Changing a viewing angle changes the relative alignment of the surface and underlying planes as well as the perceived alignment of an invasive tool perhaps being used in the procedure.
The present invention provides a new and improved IGS registration technique that overcomes the above-referenced problems and others.